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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

19586 results found.

  1. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  2. GRB 250911A: Enhanced Swift-XRT position
  3. GRB 250911A: Swift-XRT observations
  4. GRB 250911A: COLIBRÍ optical counterpart candidate
  5. GRB 250911A: Swift detection of a burst
  6. GRB 250702B: Late time Chandra observations
  7. EP250908b/EP#01709240653: Swift/UVOT Detection
  8. EP#01709240653: Swift-XRT observations
  9. GRB 250905A: Swift-BAT refined analysis
  10. GRB 250903A: Swift-XRT afterglow detection
  11. GRB 250905A: Swift-XRT refined Analysis
  12. GRB 250904A: Swift-BAT refined analysis
  13. GRB 250905A: Swift/UVOT Upper Limits
  14. GRB 250905A: Enhanced Swift-XRT position
  15. GRB 250904A: Swift/UVOT Detection
  16. GRB 250903A: Swift/UVOT detection
  17. GRB 250904A: Swift-XRT refined Analysis
  18. GRB 250905A: KAIT optical upper limit
  19. GRB 250905A: Swift detection of a burst
  20. Swift GRB250905.09: Global MASTER-Net observations report
  21. Swift GRB 250904A: Global MASTER-Net observations report
  22. GRB 250904A: Enhanced Swift-XRT position
  23. GRB 250904A: TRT optical counterpart detection
  24. GRB 250904A: Prompt enhanced Swift-XRT position
  25. GRB 250904A: Swift detection of a burst
  26. GRB 250903A: Swift-XRT observations
  27. EP250903a: Swift-XRT observations
  28. EP#01709201209: Swift-XRT observations
  29. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  30. EP250901a: Mondy, Assy and SAO RAS optical limits
  31. GRB 250901A: Swift/UVOT Upper Limit
  32. GRB 250830B: Swift-XRT afterglow detection
  33. GRB 250901A: EP-FXT follow-up observation
  34. GRB 250901A: SVOM/VT optical afterglow with VHF data
  35. GRB 250901A: Swift-XRT afterglow detection
  36. EP250901a: Swift-XRT observations
  37. GRB 250901A: LCO optical upper limit
  38. EP250827b: Swift observations of AT 2025wkm
  39. GRB 250901A: SVOM detection of a burst
  40. EP250831a: EP-FXT follow-up observation
  41. EP250831a: Swift-XRT observations
  42. GRB 250831A: Swift-XRT counterpart detection
  43. GRB 250830B: Swift-XRT observations
  44. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  45. GRB 250830B: Swift ToO observations
  46. GRB 250830B: MAXI/GSC detection
  47. GRB 250828B: Swift-BAT refined analysis
  48. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  49. Swift GRB 250828B: Global MASTER-Net observations report
  50. EP250827a: Swift/UVOT Detection
  51. GRB 250828B: Swift detection of a burst
  52. EP250827a: confirmation of optical rebrightening with LCO
  53. EP250827a: Swift-XRT counterpart detection
  54. GRB 250823A: Swift-BAT refined analysis
  55. GRB 250823A: Swift-XRT refined Analysis
  56. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  57. GRB 250823A: COLIBRÍ optical observations
  58. GRB 250823A: SVOM/VT optical observation
  59. GRB 250823A: Swift/UVOT Detection
  60. GRB 250823A: NOT optical observations
  61. GRB 250823A: Fermi GBM Observation
  62. GRB 250818B: MeerKAT Detection
  63. GRB 250823A: Enhanced Swift-XRT position
  64. GRB 250823A: LCOGT Optical Detection
  65. GRB 250823A: BOOTES6/DPRT early optical detection
  66. GRB 250823A: Liverpool Telescope optical detection
  67. GRB 250823A: Swift detection of a burst
  68. Swift GRB250823.84: Global MASTER-Net observations report
  69. GRB 250821A: Kilonova-Catcher optical upper limits
  70. EP250821a: Swift/XRT counterpart fading
  71. GRB 250821A: Swift-BAT refined analysis
  72. EP250821a: Swift/UVOT further observations.
  73. GRB 250821A: VLT/FORS2 Optical Observation
  74. GRB 250821A: GECAM-B detection
  75. EP250821a: SVOM/VT optical observation
  76. GRB 250821A: NOT z-band upper limit
  77. GRB 250821A: Swift-XRT refined Analysis
  78. Swift GRB 250821A: Global MASTER-Net observations report
  79. GRB 250821A: Enhanced Swift-XRT position
  80. GRB 250821A: Swift/UVOT Upper Limits
  81. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  82. EP250821a: Swift XRT and UVOT counterpart detection
  83. GRB 250821A: LCOGT Optical Upper Limits
  84. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  85. GRB 250821A: Prompt enhanced Swift-XRT position
  86. GRB 250821A: Swift detection of a burst
  87. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  88. GRB 250814A: Swift/UVOT Upper Limits
  89. GRB 250813B: Swift/UVOT Upper Limit
  90. IPN triangulation of GRB 250814C (short)
  91. IPN triangulation of GRB 250804B (short)
  92. GRB 250818B: Kilonova-Catcher optical afterglow detection
  93. GRB 250818A: AstroSat CZTI detection
  94. GRB 250818B: Swift/UVOT Detection
  95. GRB 250818B: SAO RAS optical observations
  96. Swift GRB 250818A: Global MASTER-Net observations report
  97. GRB 250818A: Swift-XRT refined Analysis
  98. GRB 250818A: Swift-BAT refined analysis
  99. GRB 250818B: Keck redshift of the optical afterglow
  100. GRB 250818A: Swift/UVOT Upper Limits

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